This invention relates to magnetostatic wave devices for processing high frequency signals; and, more particularly, to devices, which is capable of reducing a variation for each of frequencies within a pass band.
In the field of magnetostatic wave devices, a high frequency filter, a delay line, a resonator, and a correlator are implemented through the use of a magnetostatic wave in order to cope with high frequency signals. To implement the magnetostatic wave devices, input and output electrodes are provided on a magnetically active ferromagnetic thin film on a magnetically inactive dielectric substrate, or a ferromagnetic thin film is placed on the magnetically inactive dielectric substrate after the input and output electrodes are produced. An appropriate magnetic field is then applied for energy conversion and transmission. According to prior art, input and output electrodes are lines having same size or multiple lines. In case of multiple lines, a distance between neighboring lines is constant. For both cases, a variation of wavelength for each frequency in a desired pass band of the devices is not considered effectively, thereby providing a severe characteristic variation in the pass band. A ferromagnetic thin film is provided in one side of the magnetically inactive substrate. The ferromagnetic thin film is provided in both sides to adjust a group speed by employing magnetically different thin films. Further, there is no metal shield for electrically separating input and output portions, and a coupling between the input and output portions is generated outside the pass band, thereby transmitting energy which is not desired.
FIG. 1 illustrates a schematic diagram of a prior magnetostatic wave device shown from the top, and FIG. 2 presents the prior magnetostatic wave device in FIG. 1 shown from the front. As shown, the magnetostatic wave device includes an input transmission line 12a, an output transmission line 13a, an input energy conversion portion 12b, an output energy conversion portion 13b, and a magnetically active ferromagnetic substance 14b. The input and output lines 12a and 13b having a constant width are placed on one side of a dielectric substrate 11 whose the other side is grounded 16. The input and output energy conversion portions 12b and 13b generating energy conversion between electromagnetic wave and magnetostatic wave are composed of multiple number of lines each of which has a constant width w1 or w3, a length L1 and distances g1, g2 between neighboring lines (See FIG. 3). The ferromagnetic substance 14b is provided on a magnetically active substrate 14a. 
When a magnetic field with a magnitude larger than saturated magnetization is applied to the magnetostatic wave device, the magnetically active ferromagnetic substance 14b is saturated. When an electromagnetic wave within the frequency band can be absorbed by the magnetized ferromagnetic substance is transmitted to the input energy conversion portion 12b, the electromagnetic wave is magnetically coupled and a magnetostatic wave is generated. The magnetostatic wave is transmitted to the output energy conversion portion 13b through the magnetized ferromagnetic substance and then re-converted to the electromagnetic wave, resulting in energy transmission.
A multi-layer structure 14 including the ferromagnetic substance 14b, and end portions 15a and 15b are illustrated in FIG. 1.
Referring to FIG. 3, line structure of the input and output energy conversion portions 12b and 13b employed in the prior magnetostatic wave devices are illustrated. The energy conversion lines for electromagnetic wave and magnetostatic wave are single lines each having the constant width w1 or w3 in the direction of current flow, and multiple number of the single lines each having a length L1 are placed with a constant distance g1 or g2.
The conversion line described above is employed to select a specific frequency and is good at obtaining a narrow band characteristic. However, it lowers efficiency in selecting a specific frequency band, thereby distorting a pass band characteristic as shown in FIG. 31. Further, since there is no means to block electromagnetic wave coupling between the input and output energy conversion portions, energy is also transmitted by a transmission of the magnetostatic wave as a frequency increase. Thus, the value outside the pass band becomes high as shown in FIG. 31, thereby degrading a frequency selectivity for the device.
In addition, when ground planes are placed with a constant distance at the magnetized ferromagnetic substance as shown in FIG. 1, a group delay characteristic related to a group speed of the magnetostatic wave is not linear, thereby generating phase error.
In accordance with the prior magnetostatic wave device described above, multiple number of lines which has a constant distance between neighboring lines are employed as the input and output electrodes, thereby providing a severe variation of characteristics within the pass band. In addition, in order to increase the pass band there is needed the ferromagnetic substance having a larger width.
Further, since there is no metal shield to electrically separate the input and output energy conversion portions, the input and output energy conversion portions are coupled outside the pass band, thereby generating a larger energy transmission.
It is, therefore, an object of the present invention to provide magnetostatic wave devices for processing high frequency signals, which is capable of reducing a variation within the pass band of the device and blocking energy transmission outside the pass band by reducing energy emission on non-magnetization.
Magnetostatic wave devices of the present invention comprises: input and output electrodes for including energy conversion pattern provided in a dielectric substrate; a multi-layer magnetic substance structure placed at an upper portion of the dielectric substrate, wherein magnetically active thin film is placed at both sides of a magnetically inactive substrate; an upper shield, composed of grounded conductor, for preventing the input and output electrodes from coupling; a lower shield provided at the dielectric substrate, wherein the substrate contain a hole with the same length as the upper shield, and walls of said hole are provided with conductor; a magnetostatic wave end portion, inserted into the dielectric substrate to be placed at both end plane of the multi-layer magnetic structure, for blocking the magnetostatic wave not to reflect therefrom; and a magnetostatic wave reflector, provided in the dielectric substrate as a line whose width vary, for reflecting and selecting a desired pass band before it reaches to the magnetostatic wave end portion.